The present invention is particularly concerned with the provision of equipment for abrasive jet machining providing for employment of a jet of relatively high pressure and high velocity.
Although the equipment disclosed in the present application may be employed with a pressurized gas stream at any desired pressure, the equipment of the present invention is of special importance for use where relatively high gas pressure is contemplated.
In typical abrasive jet equipment heretofore employed, the pressure of the gas has usually been lower than about 200 PSI. For many purposes, it would be desirable to utilize a pressure running up to at least several hundred PSI.
It has been known that increasing the pressure of the gas stream in an existing feed tube and nozzle results in increase of the velocity of flow through the feed tube and the delivery nozzle. With the same pressure, if the cross-sectional flow area of the delivery nozzle were appreciably reduced, the ratio of the particles to the volume of the gas would no longer form a workable combination in relation to the gas velocity and mass of the abrasive particles. The invention contemplates reducing the crosssectional flow area of the nozzle and preferably some reduction in the cross-sectional flow area of the feed tubing. In this way appropriate conditions for the abrasion are provided notwithstanding the increase in velocity of flow.
The present invention also contemplates employment of a novel form of feed tube and delivery nozzle making practical the employment of much higher pressures than employed heretofore, and the accompanying higher velocities of flow resulting from the increase in pressure.
The various features of the present invention illustrated in the drawings and fully described hereinafter result in the provision of equipment well adapted to the handling and use of an abrasive stream at a pressure in excess of 200 PSI, for instance, of the order of 300 or 400 PSI. The equipment of the present invention may also be used at even higher pressure, running up at least to about 2000 PSI. The use of these higher pressures greatly increases the production rate of the manufacturing components, but with the prior equipment, such increases of the operating pressure is not practical for a number of reasons, especially the resultant increase in the rate of wear of various of the manufacturing components, especially the tubing through which the abrasive-laden pressurized stream is delivered.
The present invention also provides for the handling of a much wider variety of particles and particle sizes than is practicable in prior known equipment. The particles may comprise any of a wide variety of materials including for example aluminum oxide or silicon carbide.
The present invention provides a novel form of abrasive flow tubing having improved capability of handling high pressure and high velocity flow. Thus, according to the present invention, the pressurized stream of abrasive-laden gas is carried in straight line tubing preferably extended in a vertical direction, desirably vertically downwardly, from the point of development of the pressurized gas stream to the delivery orifice of the abrasive nozzle employed. This makes possible extensive increase in pressure and velocity, without correspondingly increasing the wear of the tubing.
According to the invention, this vertical abrasive delivery duct or tubing is formed of rigid material such as carbide or metal, without the employment of any zones of flexible rubber or plastic tubing of the kind heretofore employed in abrasive jet machines, in order to deliver the abrasive-laden stream from the point of generation to the point of discharge through the nozzle delivery orifice. In equipment adapted for use at pressures commonly employed, for instance up to about 100 or even 200 PSI, the abrasive delivery duct may be formed of any rigid material, such as metal tubing, but if pressures substantially in excess of 200 PSI are contemplated it is preferred to use more highly abrasive resistant materials such as carbides, for instance tungsten carbide, boron carbide or certain ceramics, such as saphire.
By the employment of the straight line, preferably downwardly extended tubing, the abrasive wear to which the tubing is subjected is reduced, even at high pressures equal to many times the pressures heretofore employed. In consequence, such tubing in the equipment of the present invention has long life, notwithstanding the employment of the high pressure and high velocity flow within the tubing.
Having in mind the foregoing straight line vertical feed of the high pressure abrasive-laden gas stream, the equipment of the present invention is arranged and mounted in a novel manner. Thus, it is contemplated according to the invention to mount the abrasive stream generating equipment itself on a base or standard with the vertical delivery nozzle projecting downwardly; and it is an object of the invention to provide a work support moveable in a horizontal plane in a zone beyond the delivery opening of the abrasive nozzle.
The invention also contemplates mounting of the abrasive jet generating equipment by a mechanism providing for vertical adjustment of the nozzle in relation to the work support.
Still further, the invention contemplates certain novel forms of controls for interrelating the motions of the work support in relation to the abrasive stream being generated, and also contemplates certain interrelated controls providing for starting and stopping of the abrasive stream, without subjecting the equipment to excessive wear, even when employing very high pressure jet flow.